Aibu to just want a nice smelling flat ?!?

Feel like I'm constantly fighting this odour battle and it drives me mad. We rent and these problems are just starting, there has been others like the boiler breaking etc but it's the odour ones that are the worst.First one admittedly is my fault, we got a dog. She's an older dog and totally house trained, due to nerves she had 2 accidents in total in 3 months ( just pee ). We cleaned it up immediately, soapy water, pet odor spray, baking soda, carpet powder the whole lot. This was on our rug. Through the day when the sun would shine in it would smell, not just of pee but just a not fresh smell and I couldn't bear to sit in the sitting room. It would randomly occur too. This week we took the rug outside ( it's still there waiting to be chucked.) I shampooed the whole carpet. I was on hands and knees with zoflora water and a sponge I did the whole floor. Then proper carpet shampoo. Then the powder, window wide wide open and we stayed out of the room for 2 days straight. Smelt fresh. Next day came home from work, window had been open and yep again the horrible smell. I've checked everywhere driving me mad I reckon it's the under lay but not sure.

Next problem, the drains. Every now and then ( seems to have started now the warmer months are here ) a rotton egg sulfur smell fills the flat. It's disgusting. I pour boiling water down the kitchen sink, bath, toilet and bathroom sink it comes from everywhere. Again it goes away if I'm lucky for half an hour. I pour drain cleaner, coke, baking soda, vinegar, bleach everything ( not all at once of course ) I am super self conscious of my flat now and don't want other people here incase any of these random smells start coming back. I have plug ins, candles, reeds everything and I am super clean so just want it to smell fresh. Please help 😭 give me suggestions 😭

Rotten egg smell from our kitchen sink turned out to be coming from the overflow hole. Get a bucket and unscrew the U-shaped pipe underneath, it's probably full of stinky gunk. Can't help with the carpet though!

Is it the carpet or is it the underlay? When you spill something or a pet/child pees on it, it can go through the carpet into the underlay, so even if you clean the carpet/top part, the underlay may still be dirty or even rotting/festering. Can you lift the carpet to check? Given the cleaning lengths you have gone to, the carpet should not smell like that anymore. If it's not the underlay, can you replace the carpet (I know you said you rent)? When carpet gets old it sometimes smells, so how old is it? If all that is impossible, I'd pay a professional carpet cleaner to come in and clean it. Their industrial cleaning methods are far deeper and more effective and suck the water back up.

The sulphur smell could be U bend, as already suggested. It can become clogged with fat.